POF-based digital I-OFDR for strain detection in road construction

We report on the development of a field-proven distributed fiber optic sensing system for structural health monitoring in road construction and civil engineering. The system is based on a cost-efficient digital incoherent optical frequency domain reflectometry (I-OFDR) for distributed strain detection along a polymer optical fiber. In this method, the strain-induced backscatter increase in a graded-index multimode perfluorinated polymer optical fiber (PF-POF) is determined by measuring the complex transfer function of the sensing fiber using a compact digital data acquisition unit. This unit replaced an oversized vector network analyzer (VNA) usually used in the I-OFDR technique making the measurement system more robust and more suitable for its use in the field, whilst at the same time providing a significant reduction of the total sensor system costs. This paper presents a successful implementation of the entire sensor concept in a real construction project for the soil reinforcement and fiber optic monitoring of a road embankment using geosynthetics with incorporated PF-POF. The presented research includes development and installation in the field of the sensors integrated geosynthetics used for ground stabilization and additionally providing fiber optic POF-based monitoring function. The publication shows first measurement results of the further developed measurement method I-OFDR conducted along the PF-POF integrated in the geosynthetics embedded into a road embankment of the federal road B91 south from Leipzig.